2005 Mercury Optimax 175 problem. Help!

Motor is a 2005 175 Optimax with 126 hrs. 25 tempest plus. WOT 5350 rpms. 24 tempest plus. WOT 5650 rpms. WOT 15 water pressure. I bought it from a friend who bought it new. He says motor has had hesitation since new (he thought it was no big deal; as you can tell by the hours he didn't use it much anyway) Motor hesitates when you get to 1500 rpms. The further you push the throttle the more the rpms drop (usually to around 1200-1300) then will eventually get past 1500 and run fine. Motor cranks great, idles great and runs great in all rpms except this one spot. Previous owner had ethanol trouble and had to replace the fuel rail last year. While this was done the plugs where changed (iridiums), water pump and gear oil. I have run quick clean since I purchased the boat. Previous owner did not run quick clean. I have also replaced the fuel line, primer bubble and fuel filter. Motor does not show any fault codes. Does not throw any warning horns. Thought it was a bad TPS. Replaced the TPS and boat now has started to hesitate worse. Sometimes taking 2-3 times of full throttle to even take off (Seems worse with full load and full live well) Dealer says would try MAP sensor next. Anyway to tell or test before spending more money on changing parts? Help or Ideas? Anyone had theirs do this? Thanks in advance!

I have. Replaced old style "red writing" line from bubble to cowling, new primer bulb and new fuel filter. Old filter looked pretty clean. Was replaced last year by previous owner when fuel rail was replaced. Did not rebuild or replace fuel pump.

Don, Thanks for your help and advise. I have done everything in that post except for rebuilding the pulse fuel pump. I will do that soon, but I think I might have figured my problem out this morning; just don't know how to fix it! Here's the latest......went fishing this morning. Motor did not hesitate at all (3/4 tank of fuel and live well was empty) Second stop filled live well with water and 2 fish.............started the 1500 rpm hesitation. Told my partner to go to front of boat, without touching the controls hesitation stops completely. When he comes back to seat starts again. Keep in mind, I have not touched the throttle the whole time. Tried this a dozen times and without fail same every time. Read in several posts about an exhaust tuner being loose or off could cause this? Seems like my hesitation starts when the motor is setting far back in the water and stops when its not, if this makes sense? How do I check to see if the exhaust tuner is loose or not hooked up? Thanks, Samuel

That could be related to the tuner being loose- but it also could be caused by a number of other items (prop, PVS openings, skewed jackplate, Exhaust Relief opening of engine sitting too low in the water, or even water weight IN the boat hull).

Easiest way to check the tuner: Drop the gearcase (like you were going to replace water pump). Reach up into the exhaust housing with a long screwdriver, and see if the exhaust tuner is FIRMLY attached to the lower adapter plate (it should not move at all).

Thanks again Don. Will check the exhaust tuner today and post back. Has the same hesitation with two different props. (one is a 24 tempest plus the other is a 25 tempest plus) Boat is a ranger 185 that does not have a jack plate but does have the set back built in the hull. Motor is mouned in the middle holes. Looks to me like it came that way from the factory since the paint around the other holes is still intact. Previous owner never left in water and kept in closed garage just as i do so I would say that there is no way to have gotten water in the hull. Maybe bad design by ranger; 40 gal fuel tank, 3 batteries, ~35 gal livewell and 2 200 pound fisherman don't mix when they are all full?

What you're trying to determine is the difference in DIAMETER between the prop and the gearcase bore (if it's not close to 1/4" or more, that's not the problem).

Just to be sure... have you parked the boat on a hill, removed the DRAIN PLUG, and poked something into the drain plug hole to make CERTAIN that there's no water there? Just 25 gallons of water is like adding another person in the boat....

No water in boat hull. Called Ranger and spoke to Bud who verified motor was rigged in correct hole and does not need raising. He said I need to run a 24" prop in the summer when i have a full livewell and full tank of gas and a partner. 25 would probably be fine in the winter or with a lighter load. Both Don and Bud said it could be my pvs plugs. I had the large ones in my 25 prop. Removed them and it did not hesitate this morning when i fished! Hope it is just a weight distribution issue and not anything wrong with the motor. I will keep u posted. Thanks for the help!

No water in boat hull. Called Ranger and spoke to Bud who verified motor was rigged in correct hole and does not need raising. He said I need to run a 24" prop in the summer when i have a full livewell and full tank of gas and a partner. 25 would probably be fine in the winter or with a lighter load. Both Don and Bud said it could be my pvs plugs. I had the large ones in my 25 prop. Removed them and it did not hesitate this morning when i fished! Hope it is just a weight distribution issue and not anything wrong with the motor. I will keep u posted. Thanks for the help!

This post has been very very very helpful. I have the same EXACT set up and have had a similar problem. Could some one please tell me what/where a pvs plug is and what it does. Is there any potential problem with removing it? Should I put it back for the winter months? I will be researching it as well. I can't thank you enough, I have already paid mechanics to problem solve this issue and they were unsuccessful. They could not do a water test because I will not put this boat in Salt water and this problem does not show up off the water. My mechanic did mention that it was a big prop, but I kind of blew it off because it came that way from the factory. Thanks again, this feels like Christmas.

PVS plugs simply adjust the amount of ventilation that occurs on holeshot. You can try ANY combination that works for your rig (solid, small, medium, large, or none). You can even mix/match, or leave some (or all) out. Whatever works for YOUR rig.

fished again this morning. Full tank of fuel, full live well and fish, partner and gear..................No hesitation at all..............amazing what removing a few pvs plugs will do! Still need to purchase a 24" prop as I can only tack 5200-5300 rpms like this. Hesitation is solved! Thanks everyone! Tight lines!